The disclosure of Japanese Patent Application No. 2002-281024 filed on Sep. 26, 2002, including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to control system and method for an internal combustion engine having a variable valve actuation system
2. Description of the Related Art
There is a known internal combustion engine having a variable valve actuation system that controls the amount of intake air by changing the open valve duration of the intake valves while keeping the throttle valve fully open so as to avoid pumping loss. In order to a accurately control the amount of intake air in such an internal combustion engine, the control instruction value for controlling the open valve duration of the intake valves needs to accurately correspond to the amount of intake air. To this end, a related-art technology holds the throttle valve at a set degree of opening, and changes the open valve duration of the intake valves on the basis of the control instruction value, and corrects the reference control instruction value on the basis of the negative pressure that occurs in the intake pipe (e.g., see Japanese Patent Application Laid-open Publication No. 6-317129).
According to the related-art technology, it is considered that the reference control instruction value is corrected on the basis of the intake pipe negative pressure that corresponds to the actual amount of intake air, and therefore that if the thus-corrected control instruction value is used as a basis for the control of the open valve duration of the intake valves, the amount of intake air can be accurately controlled.
In the related-art technology, the throttle valve does not cooperate with on an accelerator pedal, but the degree of opening of the throttle valve can be freely adjustable. As for this type of throttle valve, however, the actual degree of throttle valve opening fixed for correction of the reference control instruction value may be different from the set degree of opening. In such a case, the reference control instruction value cannot be accurately corrected, since the intake pipe negative pressure greatly changes depending on the degree of throttle valve opening as well. As a result, the control of the amount of intake air become inaccurate.
Accordingly, it is an object of the invention to enable accurate control of the amount of intake air in an internal combustion engine having a variable valve actuation system in which a throttle valve whose degree of opening is adjustable is provided, and an amount of intake air is controlled by changing the degree of opening of the throttle valve and changing at least one of the open valve duration of an intake valve and the amount of lift of the intake valve via the variable valve actuation system.
An aspect of the invention provides a control method for an internal combustion engine having (i) a throttle valve whose degree of opening is adjustable, and (ii) a variable valve actuation system which includes an intake valve and enables the degree of opening of the intake valve to be variably changed, where an amount of intake air is controlled by changing at least one of an open valve duration of the intake valve and an amount of lift of the intake valve based on a pre-set variable valve control value and by changing the degree of opening of the throttle valve based on a pre-set throttle valve control value in accordance with a state of operation of the engine. The control method is characterized as follows. That is, if during a specific steady operation state, an actual intake pipe pressure is different from a target intake pipe pressure set during the specific steady operation state, a first correction amount for one of the throttle valve control value and the variable valve control value is calculated by changing the one of the throttle valve control value and the variable valve control value so that the actual intake pipe pressure becomes equal to the target intake pipe pressure. If at this time the actual amount of intake air is still different from a target amount of intake air set during the specific steady operation state, a second correction amount for another one of the throttle valve control value and the variable valve control value is calculated by changing the another one of the throttle valve control value and the variable valve control value so that the actual amount of intake air becomes equal to the target amount of intake air. The second correction amount is used to further correct the one of the throttle valve control value and the variable valve control value corrected by the first correction amount.
In a preferred form of the above-described control method, the first correction amount and the second correction amount are updated.
In a another preferred form of the above-described control method, it is determined that the throttle valve or the variable valve actuation system has a fault, if the first correction amount is outside a threshold value range or if the second correction amount is outside a threshold value range.
Another aspect of the invention provides a control system for an internal combustion engine, which includes (i) a throttle valve whose degree of opening is adjustable, (ii) a variable valve actuation system that includes an intake valve and enables the degree of opening of the intake valve to be variably changed; and (iii) a controller that controls an amount of intake air by changing at least one of an open valve duration of the intake valve and an amount of lift of the intake valve based on a pre-set variable valve control value and by changing the degree of opening of the throttle valve based on a pre-set throttle valve control value in accordance with a state of operation of the engine. According to this system, if during a specific steady operation state, an actual intake pipe pressure is different from a target intake pipe pressure set during the specific steady operation state, the controller calculates a first correction amount for one of the throttle valve control value and the variable valve control value by changing the one of the throttle valve control value and the variable valve control value so that the actual intake pipe pressure becomes equal to the target intake pipe pressure. At this time, if the actual amount of intake air is different from a target amount of intake air set during the specific steady operation state, the controller calculates a second correction amount for another one of the throttle valve control value and the variable valve control value by changing the another one of the throttle valve control value and the variable valve control value so that the actual amount of intake air becomes equal to the target amount of intake air. Also, the controller uses the second correction amount to further collect the one of the throttle valve control value and the variable valve control value corrected by the first correction amount.
In a preferred form of the above-described control system, the controller is adapted to update the first correction amount and the second correction amount.
In another preferred form of the above-described control system, the controller is adapted to determine that the throttle valve or the variable valve actuation system has a fault, if the first correction amount is outside a threshold value range or if the second correction amount is outside a threshold value range.
In a preferred form of the above-described control system, the controller is adapted to, if the fast correction amount is outside a threshold value range or if the second correction amount is outside a threshold value range, correct the degree of opening of the throttle valve or at least one of the open valve duration of the intake valve and the amount of lift of the intake valve with a guard such that the first or second correction amount calculated at this time will not become outside a threshold value range that is narrower than the threshold value range used for the fault determination.